Naphthalimide-based multiresponsive copper metal-organic framework for ratiometric detection of ClO− and turn-on sensing Fe3+, Cr3+, and Al3+ in water

Developing a single fluorescent sensor for multi-analytes with distinguishable output signals is significant but challenging. Herein a novel 2D copper metal-organic framework, namely NBCu, has been facilely prepared based on the assembling of imidazole and morpholine functionalized 1, 8-naphthalimide, 1, 3, 5-benzenetricarboxylic acid and Cu2+ ions, which presents solvent and pH stability (2.0–12.0) and thermostability. In addition, NBCu shows a significant and selective ratiometric fluorescent response to ClO− with more than 200-fold enhancement in fluorescence ratio (F473/F394), mainly due to an inhibited photoinduced electron transfer (PET) process by the hydrogen bonding interactions between morpholine and HClO that generated from ClO− in water. Meanwhile, the ClO− detection limit is determined as 82.95 nM, and the sensor can be regenerated and reused 5 times. Moreover, NBCu exhibits selective turn-on fluorescence (F394) to Fe3+, Cr3+, and Al3+ with the detection limit down to 10−8 M level and can be reused up to 5 cycles. Turn-on sensing behaviors are mainly the result of the absorbance-caused enhancement (ACE) effect and hydrogen bond destruction related to the interactions between the metal ions and the MOF. Significantly, using real water samples, NBCu can be employed as a tracer for ClO− detection.